This invention relates to a thermal fluid sensor which can be used to discriminate the kind of fluid, a fluid identifying apparatus and method for identifying the kind of an object fluid for measurement (simply referred to as object fluid or fluid) on the basis of a temperature detected signal produced from the fluid sensor, a flow velocity sensor (simply referred to as a flow sensor) which can be used for measurement of the flow rate, and a flow rate measuring apparatus and method for measuring the flow rate of the object fluid on the basis of a temperature detected signal. More particularly, this invention relates to a flow sensor and a flow rate measuring apparatus and method which can measure the flow rate of the fluid accurately even when the kind and composition of the fluid are changed, and relates to a flow rate measuring apparatus and method which can measure the flow rate of the fluid even when the measuring range of the flow rate is relatively wide.
FIG. 9 shows an arrangement view of a conventional thermal micro-flow sensor. A micro-flow sensor 101 includes an Si substrate 102, a diaphragm 103, a micro-heater 104, a downstream thermopile 105 formed on the diaphragm 103 at the lower end of the micro-heater 104, power source terminals 106A, 106B for supplying a driving current to the micro-heater 104, an upstream thermopile 108 formed on the diaphragm 103 at the upper end of the micro-heater 104, first output terminals 109A, 109B for producing a first temperature detected signal supplied from the upstream thermopile 108, and second output terminals 107A, 107B for producing a second temperature detected signal supplied from the downstream thermopile 105.
According to the micro-flow sensor 101 thus configured, in response to the driving current supplied externally, the micro-heater 104 heats an object fluid for measurement such as a gas to generate uniform temperature distributions from itself to the downstream thermopile 105 and from itself to the upstream thermopile 108.
In this state, when the flow from P to Q is generated in the object fluid such the gas, the temperature distribution around the micro-heater is deflected downstream of the object fluid, i.e. toward the downstream thermopile 105. Therefore, the upstream thermopile 108 detects the temperature lower than when no flow is generated in the fluid, i.e. flow rate=0. Then, the upstream thermopile 108 produces the first temperature detected signal corresponding to the detected temperature.
On the other hand, the downstream thermopile 105 detects the temperature higher than when no flow is generated in the fluid, i.e. flow rate=0 by the degree the temperature distribution has been deflected downstream. Then, the downstream thermopile 105 produces the second temperature detected signal corresponding to the detected temperature. Thus, a flow rate measuring apparatus (not shown) can measure the flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal from the upstream thermopile 108 and the second temperature detected signal from the downstream thermopile 105.
However, the conventional micro-flow sensor as shown in FIG. 9 has a disadvantage that when the kind or composition of the object fluid, the output characteristic is also changed.
Specifically, when the kind or composition of the fluid, the physical property (hereinafter simply referred to as xe2x80x9cpropertyxe2x80x9d) of the fluid such as thermal conductivity, specific heat, viscosity, density, etc. is also changed. This modifies the temperature distribution of the fluid heated by the micro-heater, and hence the output characteristic.
In order to obviate such failure, aside from the micro-flow sensor, a gas analysis sensor was arranged, or otherwise the micro-flow sensor or a device incorporating it was caused to recognize the properties of the fluid previously.
However, for example, in a gas meter, the gas having the same standard has a slightly different composition of the raw gas according to various lots. The gas composition for controlling the quantity of heat is adjusted with limited accuracy by a gas production factory so that the composition of the gas having the same standard may be changed. Therefore, there was a limit for the characteristic value of the fluid to be previously recognized by the micro-flow sensor and the device incorporating it.
Where the gas analysis sensor is arranged aside, the gas meter is upsized, and the method for correcting the flow rate and the location of the gas analysis sensor must be considered. This makes it difficult to manufacture the gas meter at low cost.
This invention has been accomplished in view of the above circumstance.
An object of this invention is to provide a thermal fluid sensor and fluid identifying apparatus and method which permits a flow sensor to measure the flow rate of an object fluid accurately even when the flow sensor produces a change in the output characteristic with a change in the kind or composition of an object fluid, and also provide the flow sensor and flow rate measuring apparatus and method which is preferably used to measure the flow rate using these thermal fluid sensor and fluid identifying apparatus and method.
In order to attain the above objects, the thermal fluid sensor defined in another aspect of the invention is characterized by comprising:
a heater for heating an object fluid for measurement flowing through a flow path by a driving current externally supplied;
a side temperature sensor arranged in a direction orthogonal to the flow direction of the object fluid with respect to the heater to detect the temperature of the object fluid so that a temperature detected signal is produced; and
a supporting board for supporting the heater and the side temperature sensor.
The fluid discriminating apparatus in another aspect of the invention for discriminating the kind of the object fluid using the thermal fluid sensor is further characterized by comprising:
fluid property computing means for computing the property of the object fluid on the basis of the temperature detected signal supplied from the side temperature sensor in the thermal fluid sensor.
The fluid discriminating apparatus in another aspect of the invention for discriminating the kind of the object fluid using the thermal fluid sensor is further characterized by comprising:
flow rate measuring means for measuring the flow rate of the object fluid flowing through the fluid path;
reference range data storage means for storing data of a plurality of kinds of reference ranges of the temperature detected signal corresponding to the flow rates of the object fluid flowing through the flow path, the reference ranges being different according to the kinds of the object fluid and correlated with the kinds;
reference range data inferring means for inferring a single reference range data corresponding to the flow rate of the object fluid from data of the plurality of reference ranges stored in the reference range data storage means;
pertinent reference range determining means for determining the reference range correlated with the object fluid to which the temperature detected signal belongs,
wherein it is determined that the object fluid correlated with the reference range thus determined is the object fluid flowing through the flow path.
The fluid discriminating method in another aspect of the invention of discriminating the object fluid using the thermal fluid sensor is further characterized by comprising:
fluid-property computing step of computing the property of the object fluid on the basis of the temperature detected signal supplied from the side temperature sensor in the thermal fluid sensor.
The fluid discriminating method in another aspect of the invention for discriminating the kind of the object fluid using the thermal fluid sensor, comprises:
flow rate measuring step of measuring the flow rate of the object fluid flowing through the fluid path;
reference range data inferring means step of inferring a single reference range data corresponding to the flow rate of the object fluid from a group of data of a plurality of prescribed reference ranges of the temperature detected signal corresponding to the flow rates of the object fluid flowing through the flow path, the reference ranges being different according to the kinds of the object fluid and correlated with the kinds;
pertinent reference range determining step of determining the reference range correlated with the object fluid to which the temperature detected signal belongs,
wherein it is determined that the object fluid correlated with the reference range thus determined is the object fluid flowing through the flow path.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor is further characterized by comprising:
flow rate measuring means for measuring the flow rate of the object fluid flowing through the flow path; and
flow rate correcting means for correcting the flow rate of the fluid measured by the flow rate measuring means.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor is further characterized by comprising:
flow rate measuring means for measuring the flow rate of the object fluid flowing through the flow path;
deciding means for deciding whether the flow rate of the fluid measured by the flow rate measuring means is in a high flow rate state or a low flow rate;
flow rate outputting means for outputting an output signal from the flow rate measuring means as a flow rate detected signal as it is if the flow rate is decided to be in the low flow rate state, and another output signal when the output signal from the flow rate measuring means is divided by the temperature detected signal from the side temperature sensor if the flow rate is decided to be in the high flow rate state.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor,
flow rate measuring means for measuring the flow rate of the fluid flowing through the flow path and producing an output signal having a value corresponding to the flow rate thus measured;
fluid property computing means for computing the property of the object fluid on the basis of the temperature detected signal supplied from the side temperature sensor in the thermal fluid sensor;
parameter storage means storing a plurality of kinds of parameters each for converting the output signal from the flow rate measuring means into a flow rate; and
selecting means for selecting a single parameter of the plurality of kinds of parameters stored in the parameter storage means on the basis of the property of the object fluid computed by the fluid property computing means, wherein
the flow rate converted from the output signal from the flow rate measuring means using the single parameter selected by the selecting means is taken as the measured value of the flow rate of the object fluid flowing through the flow path.
The flow rate measuring method in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor, is further characterized by comprising:
flow rate measuring step of measuring the flow rate of the object fluid flowing through the flow path; and
flow rate correcting step of correcting the flow rate of the fluid measured by the flow rate measuring means.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor is further characterized by comprising:
flow rate measuring step of measuring the flow rate of the object fluid flowing through the flow path;
deciding step of deciding whether the flow rate of the fluid measured by the flow rate measuring means is in a high flow rate state or a low flow rate;
flow rate outputting step of outputting an output signal acquired in the flow rate measuring step as a flow rate detected signal as it is if the flow rate is decided to be in the low flow rate state, and another output signal when the output signal acquired in the flow rate measuring step is divided by the temperature detected signal from the side temperature sensor if the flow rate is decided to be in the high flow rate state.
The flow rate measuring method in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the thermal fluid sensor
flow rate measuring step of measuring the flow rate of the fluid flowing through the flow path and producing an output signal having a value corresponding to the flow rate thus measured;
fluid property computing step of computing the property of the object fluid on the basis of the temperature detected signal supplied from the side temperature sensor in the thermal fluid sensor;
selecting means for selecting a single parameter of the plurality of kinds of prescribed parameters on the basis of the property of the object fluid computed in the fluid property computing step, the plurality of kinds of parameters each for converting the output signal from the flow rate measuring means into a flow rate,
wherein the flow rate converted from the output signal from the flow rate measuring means using the single parameter selected in the selecting step is taken as the measured value of the flow rate of the object fluid flowing through the flow path.
The flow sensor defined in another aspect of the invention is characterized by comprising:
a heater for heating an object fluid flowing through a flow path by a driving current externally supplied;
an upstream temperature sensor arranged upstream of the object fluid with respect to the heater to detect the temperature of the object fluid so that a first temperature detected signal is produced;
a downstream temperature sensor arranged downstream of the object fluid with respect to the heater to detect the temperature of the object fluid so that a second temperature detected signal is produced;
a side temperature sensor arranged in a direction orthogonal to the flow direction of the object fluid with respect to the heater to detect the temperature of the object fluid so that a third temperature detected signal is produced; and
a supporting board for supporting the heater, the upstream sensor, the downstream sensor and the side temperature sensor.
The fluid discriminating apparatus in another aspect of the invention for discriminating the kind of the object fluid using the thermal fluid sensor is further characterized by comprising:
flow rate measuring means for measuring a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor;
reference value storage means for storing a plurality of kinds of reference values of the third temperature detected signal supplied from the side temperature sensor within the flow sensor, the reference values corresponding to flow rates of the object fluid flowing through the flow path;
reference value inferring means for inferring a single reference value corresponding to the flow rate of the object fluid measured by the flow rate measuring means from the plurality of kinds of reference values stored in the reference value storage means; and
temperature detected signal ratio computing means for computing a ratio of the reference value inferred by the reference value inferring means to the third temperature detected signal supplied from the side temperature sensor,
wherein the fluid property computing means computes the property of the object fluid on the basis of the ratio computed by the temperature detected signal ratio computing means.
The fluid discriminating apparatus defined in another aspect of the invention is characterized by comprising:
flow rate measuring means for measuring a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
fluid property computing means for multiplying the flow rate or its square root of the object fluid flowing through the flow path measured by the flow rate measuring means by the temperature detected signal supplied from the side temperature sensor in the flow sensor, thereby acquiring the property of the object fluid.
The fluid discriminating apparatus in another aspect of the invention for discriminating the kind of the object fluid using the flow sensor is further characterized by comprising:
flow rate measuring means for measuring a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
reference range data storage means for storing data of a plurality of kinds of reference ranges of the third temperature detected signal corresponding flow rates of the object fluid flowing through the flow path, the reference ranges being different according to the kinds of the object fluid and correlated with the kinds;
reference range data inferring means for inferring a single reference range data corresponding to the flow rate of the object fluid from data of the plurality of reference ranges stored in the reference range data storage means;
pertinent reference range determining means for determining the reference range correlated with the object fluid to which the third temperature detected signal belongs,
wherein it is determined that the object fluid correlated with the reference range thus determined is the object fluid flowing through the flow path.
The fluid discriminating method in another aspect of the invention for discriminating the kind of the object fluid using the flow sensor is further characterized by comprising;
flow rate measuring step of measuring a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor;
reference value storage step of storing a plurality of kinds of reference values of the third temperature detected signal supplied from the side temperature sensor within the flow sensor, the reference values corresponding to flow rates of the object fluid flowing through the flow path;
reference value inferring step of inferring a single reference value corresponding to the flow rate of the object fluid measured by the flow rate measuring means from the plurality of kinds of reference values stored in the reference value storage means; and
temperature detected signal ratio computing step of computing a ratio of the reference value inferred by the reference value inferring means to the third temperature detected signal supplied from the side temperature sensor,
wherein the fluid property computing means computes the property of the object fluid on the basis of the ratio computed by the temperature detected signal ratio computing means.
The fluid discriminating method in another aspect of the invention for discriminating the kind of the object fluid using the flow sensor,
flow rate measuring step for computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
fluid property computing step of multiplying the flow rate or its square root of the object fluid flowing through the flow path measured by the flow rate measuring means by the temperature detected signal supplied from the side temperature sensor in the flow sensor, thereby acquiring the property of the object fluid.
The fluid discriminating method in another aspect of the invention discriminating the kind of the object fluid using the flow sensor is further characterized by comprising:
flow rate measuring step of measuring a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
reference range data inferring step of inferring a single reference range data corresponding to the flow rate of the object fluid from data of a plurality kinds of reference ranges of the third temperature detected signal corresponding to the flow rates of the object fluid flowing through the flow path, the reference ranges being different according to the kinds of the object fluid and correlated with the kinds;
pertinent reference range determining step of determining the reference range correlated with the object fluid to which the third temperature detected signal belongs,
wherein it is determined that the object fluid correlated with the reference range thus determined is the object fluid flowing through the flow path.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor, comprises:
flow rate computing means computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
fluid property computing means for computing the property of the object fluid on the basis of the third temperature detected signal supplied from the side temperature sensor with the flow sensor; and
flow rate correcting means for correcting the flow rate of the object fluid computed by the flow rate computing means on the basis of the property of the object fluid computed by the fluid property computing means.
The flow rate measuring apparatus defined in claim 41 for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor set forth in claim 24 is characterized by comprising:
flow rate computing means for computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
deciding means for deciding whether the flow rate of the fluid measured by the flow rate measuring means is in a high flow rate state or a low flow rate;
flow rate outputting means for outputting an output signal from the flow rate measuring means as a flow rate detected signal as it is if the flow rate is decided to be in the low flow rate state, and another output signal when the output signal from the flow rate measuring means is divided by the third temperature detected signal from the side temperature sensor if the flow rate is decided to be in the high flow rate state.
The flow rate measuring apparatus defined in claim 42 for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor set forth in claim 24,
flow rate computing means for computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor and producing an output signal having a value corresponding to the flow rate thus computed;
fluid property computing means for computing the property of the object fluid on the basis of the third temperature detected signal supplied from the side temperature sensor in the flow sensor;
parameter storage means storing a plurality of kinds of parameters each for converting the output signal from the flow rate computing means into a flow rate; and
selecting means for selecting a single parameter of the plurality of kinds of parameters stored in the parameter storage means on the basis of the property of the object fluid computed by the fluid property computing means, wherein
the flow rate converted from the output signal from the flow rate measuring means using the single parameter selected by the selecting means is taken as the measured value of the flow rate of the object fluid flowing through the flow path.
The flow rate measuring method defined in claim 43 for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor set forth in claim 24 is characterized by comprising:
flow rate computing step of computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor; and
fluid property computing step of computing the property of the object fluid on the basis of the third temperature detected signal supplied from the side temperature sensor within the flow sensor;
flow rate correcting step of correcting the flow rate of the object fluid computed by the flow rate computing means on the basis of the property of the object fluid computed in the fluid property computing step.
The flow rate measuring apparatus defined in claim 45 for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor set forth in claim 24, comprising:
flow rate computing step for computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor, thereby acquiring a signal having the value corresponding to the computed flow rate; and
deciding means for deciding whether the flow rate of the fluid acquired in the flow rate measuring step is in a high flow rate state or a low flow rate;
flow rate outputting means for outputting an output signal acquired in the flow rate computing step as a flow rate detected signal as it is if the flow rate is decided to be in the low flow rate state, and another output signal when the output signal acquired in the flow rate computing step is divided by the third temperature detected signal from the side temperature sensor if the flow rate is decided to be in the high flow rate state.
The flow rate measuring apparatus in another aspect of the invention for measuring the flow rate of the object fluid flowing through the flow path using the flow sensor is further characterized by comprising:
flow rate computing step of computing a flow rate of the object fluid on the basis of a difference signal between the first temperature detected signal supplied from the upstream temperature sensor and the second temperature detected signal supplied from the downstream temperature sensor and producing an output signal having a value corresponding to the flow rate thus computed;
fluid property computing step of computing the property of the object fluid on the basis of the third temperature detected signal supplied from the side temperature sensor in the flow sensor;
parameter storage means storing a plurality of kinds of parameters each for converting the output signal acquired in the flow rate computing step into a flow rate; and
selecting step of selecting a single parameter of the plurality of kinds of parameters on the basis of the property of the object fluid computed in the fluid property computing step, wherein
the flow rate converted from the output signal from the flow rate computing step using the single parameter selected in the selecting step is taken as the measured value of the flow rate of the object fluid flowing through the flow path.